Polycrystalline soft ferrites, Mg1-xZnxFe2-ySmyO4 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0; y = 0, 0.05 and 0.10) was prepared by usual ceramic method. The single-phase spinel formation of ferrites was confirmed by X-ray diffraction technique. The dielectric measurements were carried out at room temperature as a function of frequency and composition. The experimental results reveal that dielectric constant and dielectric loss tangent decrease where as ac electrical conductivity increases as frequency increases. The ac electrical conductivity is derived from the dielectric measurements. The dielectric behavior is attributed to the Maxwell-Wagner type interfacial polarization. The conduction mechanism in these ferrites is due to electron hopping between Fe2+ and Fe3+ ions on adjacent octahedral sites. The composition dependence Of epsilon' and sigma(ac) indicate that they increase with increase in Zn ion substitution and reach a maximum value and then they decrease. The addition of Sm3+ content decreases the dielectric constant. (C) 2008 Elsevier B.V. All rights reserved.